1. Field of the Invention
This invention relates to snow removal devices and particularly to snow removal devices for relatively flat surfaces and the like.
2. Description of Related Art
Snow is an extremely variable material. It can easily range from a light fluffy material that cannot support any significant loading to wind driven and frozen material that can be sawed into blocks and used as structural building material. Its hardest form is pure ice, formed by repeated freeze thaw cycles.
In climates susceptible to winter snow falls, the loading of structures caused by the weight of the accumulated material is of major concern. Other significant factors include the ice dam effects common to roof eaves, the risk to personnel movement caused by the concealment of dangerous objects or surfaces and the risk of injury from heavy snow masses falling from above.
To alleviate these snow-related problems, snow removal devices have been created. The current art of specialized snow removal devices has primarily focused on pitched dwelling roofs. Flat roofs have been handled using tools equally suited to ground level operations, such as scoop shovels and the like.
The most common method to date for dealing with snow accumulations on pitched roofs is still for a person to climb up to, and walk on, the surface. A scoop or push shovel is then used to mechanically move the material to the edge, and let gravity pull it to the ground. Several devices have been proposed which use a cutting method followed by a friction-reducing device, such as a plastic chute, to allow the snow to slide to the eave by the force of gravity. Several of these methods use a push rod to allow the operator to remain on the ground and move the cutter through the snow mass. Others require the operator to be on the roof surface and move the cutter through the snow. Two fundamental concepts that all of these methods have in common are: (1) the assumption that the surface has a sufficient pitch that once the snow is cut and placed on the friction reducing method, it slides on its own and, (2) the snow is soft enough that the cutting edge moves easily through the snow mass.
Snow removal from flat or shallow pitch surfaces is a difficult and often dangerous task. The most common approach is to place a person on the structure and use conventional snow shovels, push scoops, or brooms to carry the material to the edge, where it is allowed to naturally fall away. This approach is fraught with potential danger to the operator and damage to the property. Deep, compacted snow coupled with fragile surfaces such as greenhouse roofs or aircraft wings can compound the problems to an almost impossible level. It should also be recognized that in many cases it is not required to remove all of the snow from the entire surface area of a given structure. If the most serious problem is removing a hazard, this may mean clearing only a local area above a door or sidewalk. To reduce the load on a roof, for example, it is only necessary to remove a part of the snowpack. Almost any surface can support a 6-inch deep layer of snow. Ice dams caused by poor venting from the eave to the attic space can often be significantly reduced by removing the snow to a depth of 1 or 2 inches a distance 3 or 4 feet from the eave.
I have divided roofs and other surfaces into two different classes for the purpose of snow removal: fragile and hazardous. Class 1 surfaces are considered fragile. The classic fragile surface is a greenhouse roof, tent, aircraft wing, or boat cover. Typical construction for green houses is a frame supporting glass or plastic panels. The panels are often capable of supporting large, well-distributed static loads. The failure mode for these structures is often not the initial breakage of the glass, but collapse of the support system. The glass cannot support high point loads however and walking or chopping at accumulated snow with hoe-type tools may break the glass. Tents, yurts, canvas boat covers, and a wide range of temporary structures covered with plastic film or tarps can also be considered in the class 1 group. These surfaces usually do not support a person under any circumstances and sag as snow accumulates. The tops of truck cabs, buses, recreational vehicles and motor homes also accumulate snow but do not support point loads well. Walking on these surfaces in cold temperatures often breaks the water proofing seals resulting in water leakage.
Aircraft wings are another class 1 surface. Most current configurations set the wings at or near a horizontal plane. Even with the general pitch from front to back, the surface does not shed snow on its own. Many older aircraft have wings covered with a cotton type fabric that is very susceptible to point loads. Certain areas of the wings are especially susceptible to damage due to snow loading. These areas are the flaps, ailerons, and the elevators of horizontal stabilizers. These are all hinged surfaces and cable tensions increase with high cantilever loading. Removal of snow accumulation in small controlled lifts reduces the chance of damage due to sudden shifts of weight, which can happen with uncontrolled movement of large blocks of snow.
Class 2 surfaces are hazardous to personnel engaged in snow removal. A large flatbed trailer with a load of pipe and rebar is typical of this class. Once the snow has covered the material, footing is difficult and the slick surfaces coupled with unknown sharp objects or gaps, make it very dangerous to walk on the trailer and remove the snow with a shovel. Metal roofs of almost any pitch are hazardous surfaces. Modern paints are very slick and even surfaces with modest pitches make it difficult to maintain footing. Shake roofs are hazardous for opposite reasons. Snow may adhere to the shakes such that, even with steep pitches, significant buildup can occur. Cornices develop at the eave and can overhang several feet. Danger to personnel, both from the static loading of the structure, and from falling snow and ice is significant.
In addition to the class 1 and 2 surfaces, another category of difficult snow removal situations exists. Confined or low headroom spaces often fill with wind blown snow. Snow may need to be removed from an area below the operator, requiring a lifting out action. Vehicles that are stuck or parked in open areas can easily fill with snow between the vehicle and the ground, with the snow packed under the vehicle being the most difficult to remove. Another example is avalanche victim rescue. If the operator cannot enter the space, a snow shovel is often very awkward and inefficient
As discussed above, there are many conditions where rake or cutter type devices are not appropriate or effective. The chopping action required for removal of all but the softest snow results in damage to the surface whether the operator stands on the surface, or below it. Hoe and rake type devices have little ability to control the cutting depth or the amount of snow to be removed. Several methods have been proposed in an attempt to protect the surface and act as aids in moving over irregularities such as shingles. Examples of hoe type devices can be found in U.S. Pat. Nos. 4,848,819, 4,550,943, 5,465,510, 4,386,474, 4,249,767 and 4,024,654.
Many surfaces do not support a person, or have pitch angles, resulting in inability to use cutters requiring the operator to be in close proximity. Examples of this type of device are found in U.S. Pat. Nos. 5,570,524, 4,669,206, 4,070,771, 4,253,257 and 4,185,403.
The other devices using a push or pull type motivation method have several limitations. These limitations result from: a) the means used to control or facilitate the travel of the loosened snow towards an edge, b) the angle of delivery of thrust, c) the force necessary for effective use, and d) precision of control of the action.
Several devices have a slide or tailpiece to facilitate movement of snow. The use of very flexible type friction reducing materials often requires a complex method of rolling the material about the cutter area, resulting in moving parts and weak structure. Hinges and cranks are susceptible to ice accumulation and jamming due to frozen material.
Some devices have the thrust directed toward the center of the cutting bar, but do not provide sufficient structural strength to accommodate hard packed or very deep snow conditions. Sufficient length of the pole and distance of the operator from the path of descending snow blocks addresses only part of the hazard to operators. Attaching the thrust tube low on the cutter bar causes the push tube to ride below the surface of the snow block being removed. Devices with that configuration can cause the falling snow mass to exert large downward loads on the handle, and pose danger to the operator. Examples of these types are found in U.S. Pat. Nos. 5,943,796, 5,524,369, 5,083,388 and 3,998,486.
Special risks and problems exist when a significant depth of snow must be removed from a roof or like surface. Extensive avalanche research has shown that slab avalanches occur most often at slope angle between 30 and 45 degrees. This corresponds to roof slopes of 7/12 to 12/12. Modem metal roof paints often shed at slopes of 4/12. Chopping at snow accumulations on these slopes with rake or hoe devices can produce shock effects that allow the snow layer bonds to break and fall away in a classic slab avalanche. The chopping action also can produce a fissure that propagates across the snow mass, releasing an unpredictable amount of snow. Key to operator safety is the ability to start by removing layers from the top of the snow surface and working towards lesser depths, or matching the depth of the effective slice to the density and depth of the snow.
The ability to balance and position the implement for effective forward or reverse thrust is essential for the health and safety of the operator. Starting the first cut at a controlled depth and preventing the cutter bar from hanging up at the eave are two difficult areas. Although several devices have attempted to address the eave problem with extension from the side supports, no other device has addressed the ability to accurately control the depth of the snow removal cut.